Fuel injection control method for gdi engine

Abstract

It is possible to ensure good starting performance and operability of an engine, reduce starting time with improved combustion stability, and improve noise vibration harshness (NVH), regardless of whether the engine is started at low temperature even if a high-pressure fuel pump in a gasoline direct injection (GDI) engine breaks, without using an additional dedicated device.

1 . A fuel injection control method for a gasoline direct injection (GDI) engine, the method comprising:
 determining whether fuel pressure is at a low level where a normal fuel pressure is not properly supplied by a high-pressure fuel pump;   setting a fuel injection end time that restricts the fuel injection end time within a range where the fuel pressure is larger than combustion chamber pressure, when the fuel pressure is at a low level;   calculating the amount of fuel right after starting that determines the fuel injection amount in a function of engine cooling water temperature and fuel pressure, independently from the normal fuel pressure right after the engine is started, when the fuel pressure is at a low level; and   calculating an advance amount of a fuel injection starting time that determines the advance amount of a fuel injection starting time in consideration of fuel injection time at low pressure taken to inject all the required fuel, when the fuel pressure is at a low level.   
     
     
         2 . The fuel injection control method for a GDI engine as defined in  claim 1 , wherein the setting a fuel injection end time sets the fuel injection end time before a time where a difference between the fuel pressure measured by a fuel pressure sensor and the combustion pressure calculated by modeling is  0  or more; and
 the combustion chamber pressure is determined by multiplying all of the intake manifold pressure, the cylinder volume efficiency, a compression ratio according to a crank angle measured by a test, and a compensation value according to a change in phase angle of an intake cam which is set by a test. 
 
     
     
         3 . The fuel injection control method for a GDI engine as defined in  claim 1 , wherein the calculating the advance amount of the fuel injection starting time calculates a required advance time of the fuel injection starting time, by subtracting the normal fuel injection time, which is determined as a function of desired pressure and the required amount of fuel from the fuel injection time at low pressure which is determined as a function of the current fuel pressure and required amount of fuel; and changes the required advance time of the fuel injection starting time into the amount of an advance angle of the fuel injection starting time, in the crank angle unit. 
     
     
         4 . The fuel injection control method for a GDI engine as defined in  claim 3 , further comprising: acquiring fuel injection starting time at low pressure in the crank angle unit, by subtracting the advance amount of the fuel injection starting time from the normal fuel injection starting time. 
     
     
         5 . The fuel injection control method for a GDI engine as defined in  claim 4 , wherein the fuel injection starting time at low pressure should be limited in a range after the intake top dead center (TDC) where the intake process starts. 
     
     
         6 . A fuel injection control method for a gasoline direct injection (GDI) engine, the method comprising:
 determining whether fuel pressure is at a low level where normal fuel pressure is difficult to be made by a high-pressure fuel pump; and   setting a fuel injection end time that restricts the fuel injection end time within a range where the fuel pressure is larger than combustion chamber pressure, when the fuel pressure is at a low level.   
     
     
         7 . The fuel injection control method for a GDI engine as defined in  claim 6 , wherein the setting a fuel injection end time sets the fuel injection end time before a time where a difference between the fuel pressure measured by a fuel pressure sensor and the combustion pressure calculated by modeling is 0 or more; and
 the combustion chamber pressure is determined by multiplying all of the intake manifold pressure, the cylinder volume efficiency, a compression ratio according to a crank angle measured by a test, and a compensation value according to a change in phase angle of an intake cam which is set by a test.   
     
     
         8 . A fuel injection control method for a gasoline direct injection (GDI) engine, the method comprising:
 determining whether fuel pressure is at a low level where normal fuel pressure is difficult to be made by a high-pressure fuel pump; and   calculating the amount of fuel right after starting that determines the fuel injection amount in a function of engine cooling water temperature and fuel pressure, independently from the normal fuel pressure right after the engine is started, when the fuel pressure is at a low level.   
     
     
         9 . A fuel injection control method for a gasoline direct injection (GDI) engine, the method comprising:
 determining whether fuel pressure is at a low level where normal fuel pressure is difficult to be made by a high-pressure fuel pump; and   calculating the advance amount of a fuel injection starting time that determines the advance amount of the fuel injection starting time in consideration of fuel injection time at low pressure taken to inject all the required fuel, when the fuel pressure is at a low level.   
     
     
         10 . The fuel injection control method for a GDI engine as defined in  claim 9 , wherein the calculating the advance amount of the fuel injection starting time calculates a required advance time of a fuel injection starting time, by subtracting the normal fuel injection time which is determined as a function of desired pressure and the required amount of fuel from the fuel injection time at low pressure which is determined as a function of the current fuel pressure and required amount of fuel; and
 changes the required advance time of the fuel injection starting time into the advance amount of the fuel injection starting time in the crank angle unit.   
     
     
         11 . The fuel injection control method for a GDI engine as defined in  claim 10 , further comprising: acquiring fuel injection starting time at low pressure in the crank angle unit, by subtracting the advance amount of the fuel injection starting time from the normal fuel injection starting time. 
     
     
         12 . The fuel injection control method for a GDI engine as defined in  claim 11 , wherein the fuel injection starting time at low pressure should be limited in a range after the intake top dead center (TDC) where the intake process starts.